[bug] Fix consumer subscribe problem for basic consume

[gaoran10]

Motivation

Currently, the async method consumer.handleFlow(DEFAULT_CONSUMER_PERMIT); in basic consume command operation doesn't handle in an async way, this may cause NPE problem in the subsequent process.

Modifications

Start handle flow after subscription adds consumer finished.

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• The default values of configurations: (yes / no)
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• The admin cli options: (yes / no)
• Anything that affects deployment: (yes / no / don't know)

Documentation

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